1. Field of the Invention
The present invention relates to a method and apparatus for detecting, in the form of absolute values, the rotating position and movement of a rotary shaft driven by, for example, a servo motor.
2. Background of the Invention
A known method of detecting, in the form of absolute values, the rotating position and movement of a rotary shaft driven by, e.g., a servo motor, utilizes a plurality of position detectors, for detecting an absolute position within one full revolution of the rotary shaft. The position detectors are arranged in series with velocity reduction for each successive detector being accomplished through a gear train. One such method is disclosed in Japanese Patent Laid-open Publication 2-4437 (1990).
FIG. 19 is a schematic view showing a first conventional rotating movement detecting apparatus utilized in the method described above. The apparatus includes a first absolute position detector 1 having a rotary shaft 1a, a second absolute position detector 2 (containing a resolver, an optical absolute value encoder, etc.), a driver gear 3 fixedly mounted to the rotary shaft 1a, and a follower gear 4 fixedly mounted to a rotary shaft 2a of the second absolute position detector 2.
Another method has been proposed in which the input is reduced with the gear train of an absolute position detector and the action of each gear is detected for measuring the input movement. Such a device is disclosed in "Sensor Technology," vol. 5, no. 12, p. 22. FIG. 20 is a schematic illustration of a conventional apparatus utilized for this method, in which an absolute position detector 1 is a resolver. Illustrated are a driver gear 3 fixedly mounted to a rotary shaft 1a of the absolute position detector 1 and first and second position detecting devices 5 and 6 for dividing one revolution into tenths at low resolution. First and second position detecting devices 5 and 6 serve in combination as a rotary differential transformer. Also, a follower gear 4 and a driver gear 7 are fixedly mounted to the rotary shaft 5a of the first position detecting device 5 and a follower gear 8 is fixedly mounted to the rotary shaft 6a of the second position detecting device 6.
Still another method in which the rotating movement in an absolute position detector is detected and recorded to a memory energized by a backup battery, is disclosed in Japanese Patent Laid-open Publication 2-90017 (1990). FIG. 21 is a schematic cross-sectional view of a detecting apparatus utilized in such a method. This apparatus includes an absolute position detector 1 comprising a rotary shaft 1a, a rotary scale 1b having slits formed therein (not shown) for generating absolute code data, a light emitting diode 1c, and a photosensitive diode 1d. A magnet mounting plate 10 is fixedly mounted to the rotary shaft 1a and carries a permanent magnet 11 thereon which is magnetized in a given direction. A magnetoresistive device 12 made of a ferromagnetic material and having a high reluctance is mounted on a printed circuit board 13 so that permanent magnet 11 passes opposite to, and at a minimal distance from, magneto resistive device 12. Also, a signal processing circuit 14 is provided having a rotation signal processor circuit 14a for processing a signal from the magnetic magnetoresistive device 12 into a rotation signal which is stored and then transmitted, an absolute position signal processor circuit 14b for processing an output signal of the photosensitive diode 1d of the absolute position detector 1, and a composite signal processor circuit 14c for combining the rotation signal with an absolute position signal within one full revolution into an output signal. In addition, a backup battery 115 is provided for supplying power to the rotation signal processor circuit 14a which may be disposed remotely from the rotating movement detecting apparatus.
Another method of detecting rotational movement is disclosed in Japanese Patent Laid-open Publication 64-54309 (1989). FIG. 22 is a schematic cross-sectional view of a conventional apparatus used in this method. FIG. 23 is a front view of a magnetic bubble device 15. As illustrated in FIG. 22, a rotary shaft 1a has a permanent magnet 11, magnetized in a given direction, mounted thereon so as to pass opposite to, and at a minimal distance from, the magnetic bubble device 15. The magnetic bubble device 15 (FIG. 23) has a tip surface 15a, a magnetic transfer pattern 15b, a bubble 15c, a magnetic inductance effect element 15d, and a bubble generator 15e. Magnetic bubble technology is known in the art. For example, page 32 of the August 1987 edition of the Hitachi catalog provides a description of a magnetic bubble memory.
The operation of the conventional apparatuses described above will be explained below. In the apparatus shown in FIG. 19, the drive gear 3 is rotated as the rotary shaft 1a rotates and thus, the follower gear 4 rotates at a lower speed. Hence, the rotary shaft 2a is rotated. The reduction ratio is 1/N, where N rotations of the rotary shaft 1a corresponds to one rotation of the shaft 2a. When the power supply is on, an absolute position signal of the absolute position detector 1 and its repeated signals are processed to detect the number of rotations and the angular position of the rotary shaft 1a.
If the rotary shaft 1a is rotated accidentally during a time when the power supply is off, the apparatus will produce an absolute position signal from the absolute position detector 1 upon being energized. Simultaneously, an absolute position signal from the second absolute position detector 2 is produced and then, the rotating movement of the rotary shaft 1a is calculated based upon the absolute position signals and the reduction ratio to find a number of full rotations and the number of degrees of partial rotation.
In the apparatus shown in FIG. 20, the rotation of the rotary shaft 1a is transmitted through the driver gear 3 and the follower gear 4 to the rotary shaft 5a and simultaneously, through the driver gear 7 and the follower gear 8 to the rotary shaft 6a. If the reduction ratio is 1/N for each driver to follower interface, N.sup.2 rotations of the rotary shaft 1a corresponds to N rotations on the shaft 5a and one rotation on the shaft 6a. If the rotary shaft 1a is rotated accidentally while the power is off, the apparatus will produce, upon being energized, an absolute position signal with the absolute position detector 1 and two other absolute position signals with the first and second position detecting devices 5 and 6. These absolute position signals are then examined with respect to the reduction ratios so that the rotating movement of the rotary shaft 1a can be determined.
In the apparatus shown in FIG. 21, the light emitting diode 1c emits a light when the power supply is on and the emitted light passes through the slit in the rotary scale 1b and to the photosensitive diode 1d. As the rotary shaft 1a rotates, an output signal of the photosensitive diode 1d is varied depending on the rotating position. The repeating pattern of the output signal is then counted to produce a rotation signal from which the number of full rotations and the angular position of the rotary shaft 1a can be measured.
When the power supply is off, the rotation of the permanent magnet 11 mounted on the rotary shaft 1a varies a resistance of the magnetoresistive effect device 12 which is energized by the backup battery 115. Then, the resultant resistance variation is processed and stored by the rotation signal processor circuit 14a which is also energized by the backup battery 115. Hence, the procedure begins with a connection of the power supply and subsequently carries out the steps of turning on the light emitting diode 1c, latching the absolute position signal in response to an output signal of the photosensitive diode 1d, latching the rotation signal stored in the rotation signal processor circuit 14a, and combining the two signals with the composite signal processor circuit 14c for calculation of the number of full rotations and the angular position of the rotary shaft 1a.
In the apparatus shown in FIGS. 22 and 23, the rotating movement of the rotary shaft 1a is detected and stored using the magnetic bubble device 15. More specifically, a magnetic field is imposed vertical to the tip surface 15a by a permanent magnet (not shown) provided in the magnetic bubble device 15 and a current is applied to the bubble generator 15e for producing a bubble 15c. As the rotary shaft 1a rotates during an off state of the power supply, the rotation of the permanent magnet 11 causes the bubble 15c to be carried pattern by pattern throughout the transfer pattern 15b by the force due to magnetic flux leakage. In order to produce a rotation signal, a coil (not shown) wound on the magnetic bubble device 115 is energized by connecting the power supply to produce a rotating magnetic field which in turn actuates the bubble 15c to move to the magnetoresistive element 15d in order to read the original position of the bubble 15c.
The first apparatus (FIG. 19) employing a plurality of absolute position detectors for velocity reduction through a gear train is problematic in both size and production cost because the absolute position detectors are bulky and expensive and the gears must be formed by a costly precision machining process in order to limit relative rotating movement therebetween.
The second apparatus (FIG. 20) employing one absolute position detector for detecting the rotating action of each gear in the gear train is also costly because precision machined gears are still required, although the permitted relative rotating movement can be increased. Such a device is also large and is expensive to produce.
The third apparatus (FIG. 21) in which the rotating action in the absolute position detector is measured and stored to a memory which is energized by a backup battery is smaller in size and lower in cost. However, the backup battery, which is an extra requirement, has a limited operational life and must be replaced from time to time, even when a high resistance type of magnetoresistive device and a C-MOS type rotation signal processor circuit are used for energy saving.
The fourth apparatus (FIGS. 22-23) in which the rotating movement is detected with the magnetic bubble device is smaller in the size and lower in cost and requires no backup battery. However, the rotating magnetic field imposed to the tip surface of the magnetic bubble device must be uniform and consistent for proper transfer of the bubble. Otherwise, the operational reliability of the apparatus will be adversely affected. Accordingly such devices are not reliable.